By Sue Emmett
Senior transport producer, BBC News
It's just over a week since the BBC started a unique road charging experiment - putting to the test the government's radical proposals to cut traffic congestion - and it's proving to be an entertaining experience.
"White van man" Steve Coape-Arnold is racking up the miles
Our four "guinea pigs" are motorists living in the Midlands, driving on some of the most congested roads outside London.
Their vehicles have been fitted with Navman satellite tracking navigation systems so we can monitor and calculate the potential cost of their journeys under a road charging scheme.
Our four drivers have been going about their normal daily business blissfully unaware of how much money they could be racking up on tolls.
Whilst we are not going to reveal all the "secrets" of our experiment so far - so as not to influence how our motorists drive - we can report that there are some shocks and surprises.
Our "white van man", Steve Coape-Arnold, is already at the top of the table, having done an incredible 1,500 miles in the past week and a half.
His potential bill for just one day when he got caught in the rush hour was more than £16.
Although he fears that road charging could have a detrimental effect on his business - and the Midlands could be one of the areas chosen for a pilot scheme backed by the government - he's been trying to push it to the back of his mind.
Steve says: "I've tried to get on with it and not think about the experiment. Though sometimes when I've been in a city or on a motorway I have wondered what I might be being charged."
On the other hand our "rural driver", florist Margaret Walsh, has done quite a lot of mileage.
But she's fortunate enough to be on the quiet lanes of Staffordshire and Derbyshire and her bills are much more modest.
Margaret is worried that a charging scheme might put her out of business but she acknowledges: "My mileage can clock up but it's mostly on country roads without much congestion.
"The worst jams are when I'm delivering to Alton Towers in the summer. It's along a narrow road, so we just have to get there early before the families arrive otherwise we can get stuck for hours."
Our "school run mum", Karen Cross, thinks she doesn't use her car very often.
But when she sees the results of our experiment she may find that those little trips do add up, especially as many of them are at peak times in the city.
When she gets her final "bill" she could be in for a shock!
But do our motorists think road charging would alter the way they drive and encourage them to ditch their four wheels for public transport?
Nick Waddington does a mammoth commute by car to the Birmingham offices of Knight Frank surveyors every day from his home in Worcestershire.
So far, he's doubtful. "There are benefits to having the car. It's quicker door to door and I do need my car once I'm in the office to visit sites for building inspections.
"But since starting the study I've noticed how busy the roads are - and there are a lot of people who drive to work who probably don't need to."
There are many issues to be resolved before a road charging experiment could go ahead for real.
One big problem is privacy. The technology enables us to "spy" on our motorists.
We know when Margaret the florist has stopped off to walk her dog, when Steve the white van man is having a lie-in and we can tell when Nick the surveyor has gone to London to see "the boss" - leaving his car at the office all day as he takes the train.
Our "guinea pigs" have agreed to undergo this kind of scrutiny for the purpose of the experiment.
But they all say they would be worried if the government was to introduce a similarly run scheme.
They fear that the information - even if encoded - could fall into the "wrong hands".
Or indeed the "right hands", depending on your view, if you have committed a traffic offence such as speeding or parking on double yellow lines for example.